#include<bits/stdc++.h>
using namespace std;
const int N=1e6+7;
const int INF=0x7f7f7f7f;
int m,n,k,p,s,t,cnt=1,ans,tot;
int dx[9]={0,-3,-3,-1,-1,1,1,3,3},dy[9]={0,-1,1,-3,3,-3,3,-1,1};
struct node
{int nx,to,flow;
} e[N];
int id(int x,int y) {return (x-1)*m+y;}
int dep[N],head[N];
void add_edge(int a,int b,int flow)
{cnt++;e[cnt].flow=flow;e[cnt].nx=head[a];e[cnt].to=b;head[a]=cnt;cnt++;e[cnt].flow=0;e[cnt].nx=head[b];e[cnt].to=a;head[b]=cnt;
}
bool used[210][210];
bool bfs(int s,int t)
{queue<int> que;memset(dep,0,sizeof(dep));que.push(s);dep[s]=1;while (!que.empty()){int x=que.front();que.pop();for (int i=head[x];i;i=e[i].nx){int y=e[i].to;if (dep[y]==0&&e[i].flow){dep[y]=dep[x]+1;que.push(y);}}}if (dep[t]==0) return false;else return true;
}
int dfs(int x,int limit,int t)
{if (x==t) return limit;int used=0;for (int i=head[x];i;i=e[i].nx){int y=e[i].to;if (dep[y]==dep[x]+1&&e[i].flow>0){int di=dfs(y,min(limit-used,e[i].flow),t);if (di>0){e[i].flow-=di;e[i^1].flow+=di;used+=di;if (used==limit) return used;}}}if (!used) dep[x]=-2;return used;
}
void dinic(int s,int t)
{while (bfs(s,t)) {ans+=dfs(s,INF,t);tot++;}
}
int main()
{scanf("%d%d%d",&n,&m,&p);s=N-3;t=N-4;for (int i=1;i<=p;i++){int x,y;scanf("%d%d",&x,&y);used[x][y]=true;}for (int i=1;i<=n;i++)for (int j=1;j<=m;j++)if (!used[i][j]){if (i%2==1) add_edge(s,id(i,j),1);else add_edge(id(i,j),t,1);}for (int i=1;i<=n;i++)for (int j=1;j<=m;j++){if (i%2!=1) continue;for (int k=1;k<=8;k++){int x=i+dx[k],y=j+dy[k];if (x<=0||y<=0||x>n||y>m) continue;if (used[x][y]) continue;add_edge(id(i,j),id(x,y),INF);}}dinic(s,t);printf("%d",n*m-ans-p);return 0;
}